Composition Design And Performance Optimization Of New Types Of Fe-based Amorphous Nanocrystalline Soft Magnetic Alloys

In last decades,miniaturization and lightweight have been more important for electromagnetic device with the development of electronics industry,which requires the higher performance like high saturation magnetic induction B_s,low coercivity H_cand high maximum permeability?_mfor soft magnetic materials.Fe base amorphous and nanocrystalline alloys have attracted much attention due to their excellent soft magnetic properties.Unfortunately,relatively low B_srestricted their application,even though they have extremely low H_c.In this research,a series of works have been done to focus on the improvement of comprehensive soft magnetic properties for Fe base amorphous and nanocrystalline alloys.There are many ways of improving the soft magnetic properties of Fe base amorphous and nanocrystalline alloys.Firstly,primary crystalline phase has been changed by alloying elements,thus a new primary crystalline phase with high magnetic moment was obtained to enhance the B_s.Then,based on the initial studies,raising the content of Fe was the other way to further improve B_s.Besides,the effect of new primary crystalline phase on the H_cand?_mhas also been investigated.The main works are given as follow:1.Firetly,the effect of the content of element on the primary crystalline phase has been investigated by tuning the composition of FeBNbCu alloy.It was found,excess B content leads to the precipitation of?Fe,Nb?₂₃B₆phase which deteriorates the soft magnetic properties of the alloy due to its paramagnetic property.As a result,an appropriate B content is necessary for designing the optimum alloy composition to guarantee the precipitation of?-Fe during annealing the alloys.In this paper,H_cof Fe₇₇B₂₀Nb₂Cu₁alloy first decreases and then increases with raising annealing temperature.The optimum H_cof 7 A/m was obtained in the alloy annealed at 530?for 3 min.2.The effect of Ga addition on the primary crystalline phase of FeBNbCu alloy has been studied.The‘double crystal nucleus'during crystallization was proposed,which is that both Fe-Ga clusters embedded in the amorphous matrix and the Cu clusters precipitated at the beginning of crystallization provide nucleation sites for the precipitation of?-Fe.Optimum soft magnetic properties with saturation magnetization of 167 emu/g?1.5 T?and coercivity of 6.8 A/m was obtained in the Fe₇₅Ga₆B₁₅Nb₃Cu₁ribbon with the grain size of 8 nm that annealed at 490?for 3 min at the heating rate of 100 K/min.3.Based on the Finemet alloy,a new Fe base amorphous and nanocrystalline alloy was obtained by substituted partial Si for Ga to verify if the‘double crystal nucleus'suitable for use in the Finemet alloys.Besides,the effect of Ga addition on the primary crystalline phase,thermodynamic property and soft magnetic properties has been investigated.Compared to the FINEMET alloy,the substitution of 6 at.%Si by Ga can increase the B_sby 11.4 percent while the H_cstays the same value.The optimal magnetic properties with coercivity of 0.24 A/m and saturation magnetization of 1.37 T were obtained in the Fe_73.5Si_7.5Nb₃B₉Cu₁Ga₆ribbon.4.For the new Finemet-like alloy,Cu and Nb was substituted by Fe for further enhancing B_s.The effect of annealing condition on the microstructure and soft magnetic properties of Fe_77.5Si_7.5Ga₆B₉ribbon has been studied.It was found that,critical phase separation was detected in amorphous and annealed ribbons due to the poor glass forming ability of the alloy.When the crystallized fraction is relatively low,Fe_77.5Si_7.5Ga₆B₉ribbon with B_sof 1.5 T and H_cof 2.3A/m are obtained.Meanwhile,compared to the ribbon with high crystallized fraction,?_mis the same as the ribbon with low crystallized fraction.5.Core magnetic powders were prepared by pressing Fe₇₅Ga₆B₁₅Nb₃Cu₁and Fe_73.5Si_7.5Nb₃B₉Cu₁Ga₆powders that obtained by mechanical ball milling.After annealed at optimum annealing condition,the magnetic properties including Q,effective permeability and core loss for the two types of core magnetic powders were compared to the Fe Si B core magnetic powders than prepared by commercialization powers.The results show that,the highest effective permeability,about 28,was obtained in the Fe Ga BNb Cu core magnetic powders,which may benefit from the?-Fe?Ga?phase.Thus,Ga addition has the potential to improve the effective permeability of Fe base core magnetic powders.